Use of high-speed communication has been recently expanded through mobile devices typified by smartphones in addition to popularization of broadband lines, and thereby demand for data communication in an optical communication network goes on increasing. To meet the demand for this communication, speed-up is advanced to transmission systems of 40 Gb/S and 100 Gb/S from a transmission system of 10 Gb/S having been used until now.
International Publication No. 2014/076813 (Patent Document 1) discloses a Mach-Zehnder type optical modulator that includes a silicon optical waveguide element(s) having a rib structure.